title: Completion of biosynthetic pathways for bacteriochlorophyll g in Heliobacterium modesticaldum: The C8-ethylidene group formation.
abstract: Heliobacteria have the simplest photosynthetic apparatus, i.e., a type-I reaction center lacking a peripheral light-harvesting complex. Bacteriochlorophyll (BChl) g molecules are bound to the reaction center complex and work both as special-pair and antenna pigments. The C8-ethylidene group formation for BChl g is the last missing link in biosynthetic pathways for bacterial special-pair pigments, which include BChls a and b as well. Here, we report that chlorophyllide a oxidoreductase (COR) of Heliobacterium modesticaldum catalyzes the C8-ethylidene formation from 8-vinyl-chlorophyllide a, producing bacteriochlorophyllide g, the direct precursor for BChl g without the farnesyl tail. The finding led to plausible biosynthetic pathways for 8(1)-hydroxy-chlorophyll a, a primary electron acceptor from the special pair in heliobacterial reaction centers. Proposed catalytic mechanisms on hydrogenation reaction of the ethylidene synthase-type CORs are also discussed.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan. yusuke-t@fc.ritsumei.ac.jp
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsukatani
authors.forename: Haruki
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Fujita
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000378:metabolism*; D053898:Biosynthetic Pathways; D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D002735:Chlorophyllides / Q000378:metabolism*; D003001:Cloning, Molecular; D006094:Gram-Positive Bacteria / Q000378:metabolism*; D015394:Molecular Structure; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002735:Chlorophyllides; D002734:Chlorophyll; D044925:Oxidoreductases Acting on CH-CH Group Donors; D000077194:Chlorophyll A
keywords: 81-OH-Chl; 81-hydroxy-chlorophyll; BChl; BChlide; BPheoide; Bacteriochlorophyll; Bacteriopheophorbide; COR; Chlide; Chlorophyll; Chlorophyllide a oxidoreductase; Heliobacteria; Nitrogenase-like enzyme; Pheoide; Photosynthetic reaction center; RC; bacteriochlorophyll; bacteriochlorophyllide; chlorophyllide; chlorophyllide a oxidoreductase; pheophorbide; reaction center